Association of circulating monocyte number and monocyte–lymphocyte ratio with cardiovascular disease in patients with bipolar disorder

Background: Cardiovascular disease (CVD) is the leading cause of excessive and premature mortality in patients with bipolar disorder (BD). Despite immune cells participating considerably in the pathogenesis of CVD, limited data are available regarding leukocyte phenotypes in patients with BD and CVD. This study aimed to evaluate associations between circulating leukocyte subset and CVD among patients with BD. Methods: A total of 109 patients with BD-I and cardiologist-confirmed CVD diagnosis (i.e., case) were matched with 109 BD-I patients without CVD (i.e., control) according to the age (± 2 years), sex, and date of most recent psychiatric admission because of acute mood episode (± 2 years). Leukocyte subset data were retrieved from complete blood count tests performed on the next morning after the most recent acute psychiatric admission. Results: During the most recent acute psychiatric hospitalization, circulating monocyte counts in the case group were significantly higher than those in the age- and sex-matched controls (p = 0.020). In addition, monocyte–lymphocyte ratios (MLRs) in the case group were significantly higher than those in the control group (p = 0.032). Multiple logistic regression showed that together with serum levels of uric acid and manic symptoms, circulating monocyte counts (95% CI, OR: 1.01–1.05) and MLRs (95% CI, OR: 1.01–1.09) were significantly associated with CVD in patients with BD, respectively. Conclusions: Monocyte activation in an acute manic episode may play a critical role in the pathogenesis of CVD among patients with BD. Future research is required to investigate markers of monocyte activation and indices of cardiovascular structure and function across the different mood states of BD.